feature: port the feed page and item row to React (Phase 2b)

[vibhaseshadri-cognition]

Summary

Phase 2b of the Angular → React migration: ports feeds/feed and feeds/item from src/app/ into web/, replacing the FeedPage placeholder and adding web/src/feeds/Item.tsx. DOM structure, class names, copy and SCSS are kept identical to the Angular templates so both apps render the same markup.

Behavioural notes worth calling out (all mirror the Angular components rather than "fixing" them):

• FeedPage re-fetches on feedType/:page change and follows the RxJS semantics of the original: window.scrollTo(0, 0) runs only on the success path (the Angular complete callback never fires after an error), and the error path only sets Could not load ${feedType} stories.
• The loading/error/loaded rendering keeps the original three-way condition — !items && errorMessage === '' → <Loader />, !items && errorMessage !== '' → <ErrorMessage /> — so a failed page shows the error, not an infinite loader.
• The *ngIf="feedType !== 'new'" guard around the <ol> is preserved verbatim even though no route uses a new feed type (routes use newest).
• listStart = (pageNum - 1) * 30 + 1 drives both the <ol start> rank numbering and the prev-link visibility (listStart !== 1); More › shows only for a full 30-item response.
• Item maps hasUrl = item.url?.indexOf('http') === 0 to an external <a href> (plus (domain)), otherwise an internal /item/:id link. Angular's routerLinkActive="active" is reproduced with NavLink, which appends active for the current route. Job items drop user/points/comment links in both the palm and laptop subtexts.
• Settings are read through useSettings(): titleFontSize → title font-size, listSpacing → wrapper margin-bottom, openLinkInNewTab → target="_blank"/rel="noopener" (attributes omitted entirely when off, as [attr.x]="null" does).

feed.component.scss and item.component.scss are copied verbatim with only the @import paths rewritten to ../styles/*.

Tests

web/src/pages/FeedPage.test.tsx (11) and web/src/feeds/Item.test.tsx (11) cover loading, loaded list + rank numbering across pages, default page when :page is absent, error copy, pagination boundaries (page 1 hides prev, 30 items shows More ›, 29 hides it), navigating to page 2 refetching, jobs blurb + missing list-margin, url vs non-url vs missing-url items, job items, discuss vs n comments, and the new-tab/font-size/spacing settings. npm run lint, npm test (49 passing) and npm run build all pass in web/.

Link to Devin session: https://app.devin.ai/sessions/2725efbf76454adaa9c4123226acf5b3
Requested by: @vibhaseshadri-cognition

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